import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;

/**
 * Created with IntelliJ IEDA.
 * Description:
 * User:86186
 * Date:2023-12-21
 * Time:20:48
 */
public class UdpEchoServer {
    private DatagramSocket socket = null;

    // 参数的端口表示咱们的服务器要绑定的端口
    public UdpEchoServer(int port) throws SocketException {
        socket = new DatagramSocket(port);// 当前进程和端口就绑定起来了

    }

    // 通过这个方法启动服务器
    public void start() throws IOException {
        System.out.println("服务器启动");
        while (true) {
            // 服务器不确定客户端什么时候发送请求，要随时严阵以待
            // 循环处理一次请求
            // 1.读取请求并解析
            DatagramPacket requestPacket = new DatagramPacket(new byte[4096], 4096);
            socket.receive(requestPacket);
            // 把 DatagramPacket 转成字符串
            String request = new String(requestPacket.getData(), 0, requestPacket.getLength());
            // 2.根据请求计算响应
            String response = process(request);
            // 3.把响应写回到客户端
            DatagramPacket responsePacket = new DatagramPacket(response.getBytes(), response.getBytes().length,
                    requestPacket.getSocketAddress());
            socket.send(responsePacket);
            // 4.打印一个日志，记录当前的情况
            System.out.printf("[%s:%d] req:%s;resp:%s\n", requestPacket.getAddress().toString(),
                    requestPacket.getPort(), request, response);
        }
    } 

    // 回显服务器
    // 响应数据就和请求相同
    private String process(String request) {
        return request;
    }

}
